Oxidative Damages on the Alzheimer's Related-Aß Peptide Alters Its Ability to Assemble.

Oxidative stress that can lead to oxidation of the amyloid-ß (Aß) peptide is considered a key feature in Alzheimer's disease (AD), influencing the ability of Aß to assemble into ß-sheet rich fibrils that are commonly found in senile plaques of AD patients. The present study aims at investigating the fallouts of Aß oxidation on the assembly properties of the Aß peptide. To accomplish this, we performed kinetics and analysis on an oxidized Aß (oxAß) peptide, resulting from the attack of reactive oxygen species (ROS) that are formed by the biologically relevant Cu/Aß/dioxygen/ascorbate system. oxAß was still able to assemble but displayed ill-defined and small oligomeric assemblies compared to the long and thick ß-sheet rich fibrils from the non-oxidized counterpart. In addition, oxAß does affect the assembly of the parent Aß peptide. In a mixture of the two peptides, oxAß has a mainly kinetic effect on the assembly of the Aß peptide and was able to slow down the formation of Aß fibril in a wide pH range [6.0-7.4]. However, oxAß does not change the quantity and morphology of the Aß fibrils formed to a significant extent. In the presence of copper or zinc di-cations, oxAß assembled into weakly-structured aggregates rather than short, untangled Cu-Aß fibrils and long untangled Zn-Aß fibrils. The delaying effect of oxAß on metal altered Aß assembly was also observed. Hence, our results obtained here bring new insights regarding the tight interconnection between (i) ROS production leading to Aß oxidation and (ii) Aß assembly, in particular via the modulation of the Aß assembly by oxAß. It is the first time that co-assembly of oxAß and Aß under various environmental conditions (pH, metal ions …) are reported.

Why the Ala-His-His Peptide Is an Appropriate Scaffold to Remove and Redox Silence Copper Ions from the Alzheimer's-Related Aß Peptide.

The progressive, neurodegenerative Alzheimer's disease (AD) is the most widespread dementia. Due to the ageing of the population and the current lack of molecules able to prevent or stop the disease, AD will be even more impactful for society in the future. AD is a multifactorial disease, and, among other factors, metal ions have been regarded as potential therapeutic targets. This is the case for the redox-competent Cu ions involved in the production of reactive oxygen species (ROS) when bound to the Alzheimer-related Aß peptide, a process that contributes to the overall oxidative stress and inflammation observed in AD. Here, we made use of peptide ligands to stop the Cu(Aß)-induced ROS production and we showed why the AHH sequence is fully appropriate, while the two parents, AH and AAH, are not. The AHH peptide keeps its beneficial ability against Cu(Aß)-induced ROS, even in the presence of ZnII-competing ions and other biologically relevant ions. The detailed kinetic mechanism by which AHH could exert its action against Cu(Aß)-induced ROS is also proposed.

Keggin-type polyoxometalates as Cu(II) chelators in the context of Alzheimer's disease.

Two Keggin polyoxometalates were used as new copper ligands to counteract the effects of CuII(Amyloid-ß) interaction. Their ability to remove CuII from CuII(Amyloid-ß), to stop CuII(Amyloid-ß) induced formation of reactive oxygen species and to restore apo-like self-assembly of CuII(Amyloid-ß) was shown.

A Water-Soluble Peptoid Chelator that Can Remove Cu2+ from Amyloid-ß Peptides and Stop the Formation of Reactive Oxygen Species Associated with Alzheimer's Disease.

Cu bound to amyloid-ß (Aß) peptides can act as a catalyst for the formation of reactive oxygen species (ROS), leading to neuropathologic degradation associated with Alzheimer's disease (AD). An excellent therapeutic approach is to use a chelator that can selectively remove Cu from Cu-Aß. This chelator should compete with Zn2+ ions (Zn) that are present in the synaptic cleft while forming a nontoxic Cu complex. Herein we describe P3, a water-soluble peptidomimetic chelator that selectively removes Cu2+ from Cu-Aß in the presence of Zn and prevent the formation of ROS even in a reductive environment. We demonstrate, based on extensive spectroscopic analysis, that although P3 extracts Zn from Cu,Zn-Aß faster than it removes Cu, the formed Zn complexes are kinetic products that further dissociate, while CuP3 is formed as an exclusive stable thermodynamic product. Our unique findings, combined with the bioavailability of peptoids, make P3 an excellent drug candidate in the context of AD.

The Aggregation Pattern of Aß1-40 is Altered by the Presence of N-Truncated Aß4-40 and/or CuII in a Similar Way through Ionic Interactions.

Alzheimer's disease (AD) is one of the most common of the multifactorial diseases and is characterized by a range of abnormal molecular processes, such as the accumulation of extracellular plaques containing the amyloid-ß (Aß) peptides and dyshomeostasis of copper in the brain. In this study, we have investigated the effect of CuII on the aggregation of Aß1-40 and Aß4-40 , representing the two most prevalent families of Aß peptides, that is, the full length and N-truncated peptides. Both families are similarly abundant in healthy and AD brains. For either of the studied peptides, substoichiometric CuII concentrations accelerated aggregation, whereas superstoichiometric CuII inhibited fibril formation, likely by stabilizing the oligomers. The addition of either Aß4-40 or substoichiometric CuII affected the aggregation profile of Aß1-40 , by yielding shorter and thicker fibrils; amorphous aggregates were formed in the presence of a molar excess of CuII . The similarity of these two effects can be attributed to the increase in the positive charge on the Aß N terminus, caused both by CuII complexation and N truncation at position 4. Our findings provide a better understanding of the biological Aß aggregation process as these two Aß species and CuII coexist and interact under physiological conditions.

Copper-Targeting Approaches in Alzheimer's Disease: How To Improve the Fallouts Obtained from in Vitro Studies.

According to the amyloid cascade hypothesis, metal ions, mainly Cu and Zn ions, bound to the amyloid-ß (Aß) peptides are implicated in Alzheimer's disease (AD), a widespread neurodegenerative disease. They indeed impact the aggregation pathways of Aß and are involved in the catalytic generation of reactive oxygen species (ROS) that participate in oxidative stress, while Aß aggregation and oxidative stress are regarded as two key events in AD etiology. Cu ions due to their redox ability have been considered to be the main potential therapeutic targets in AD. A considerable number of ligands have been developed in order to modulate the toxicity associated with Cu in this context, via disruption of the Aß-Cu interaction. Among them, small synthetic ligands and small peptide scaffolds have been designed and studied for their ability to remove Cu from Aß. Some of those ligands are able to prevent Cu(Aß)-induced ROS production and can modify the aggregation pathways of Aß in vitro and in cellulo. Examples of such ligands are gathered in this Viewpoint, as a function of their structures and discussed with respect to their properties against Cu(Aß) deleterious fallouts. Nevertheless, the beneficial activities of the most promising ligands detected in vitro and in cellulo have not been transposed to human yet. Some parameters that might explain this apparent contradiction and key concepts to consider for the design of "more" efficient ligands are thus reported and discussed. En passant, this Viewpoint sheds light on the difficulties in comparing the results from one study to another that hamper significant advances in the field.

Functional modeling of the MnCAT active site with a dimanganese(III) complex of an unsymmetrical polydentate N3O3 ligand.

A new diMnIII complex, [Mn2L(OAc)2(H2O)](BPh4)·3H2O (1), obtained with the unsymmetrical N3O3-ligand H3L = 1-[N-(2-pyridylmethyl),N-(2-hydroxybenzyl)amino]-3-[N'-(2-hydroxybenzyl),N'-(benzyl)amino]propan-2-ol, has been prepared and characterized. The unsymmetrical hexadentate ligand L3- leads to coordination dissymmetry (dissimilar donor atoms) around each Mn ion (N2O4 and NO4(solvent), respectively) leaving one labile site on one of the two Mn ions that facilitates interaction of the metal center with H2O2, as in Mn catalase. 1 is able to catalyze H2O2 disproportionation in acetonitrile, with second-order rate constant kcat = 23.9(2) M-1 s-1. The accessibility of the MnII2 state and the closeness of the two one-electron reduction processes suggest 1 employs MnIII2/MnII2 oxidation states for catalysis.

The nickel(II) complex of guanidinium phenyl porphyrin, a specific G-quadruplex ligand, targets telomeres and leads to POT1 mislocalization in culture cells.

With the aim of finding selective and biologically active G-quadruplex ligands, modified porphyrin with bulky cationic substituents, meso-5,10,15,20-tetrakis(4-guanidinophenyl)porphyrin tetrahydrochloride, referred to as guanidinium phenyl porphyrin, was prepared. The corresponding nickel(II) and cobalt(III) metallated porphyrins were also synthesized. Interaction with quadruplexes was examined by means of fluorescence resonance energy transfer melting and surface plasmon resonance-based assays: the three compounds proved to bind to G-quadruplex DNA in a similar and highly selective way. Guanidinium phenyl porphyrin and its nickel(II) metallated derivative exhibit moderate cytotoxicity toward cells in culture. Strikingly, the nickel porphyrin derivative was able to displace hPOT1 shelterin protein from telomeres in human cells. Nickel(II) guanidinium phenyl porphyrin, a cationic bulky porphyrin is a powerful specific G-quadruplex DNA ligand. It enters the cells and induces shelterin modification.

Cobalt(III)porphyrin to target G-quadruplex DNA.

G-quadruplex DNA ligands attract much attention because of their potential use in biology. Indeed they may interfere with G-quadrulex nucleic acid function in cells. Most of the G-quadruplex ligands so far reported (including also metal complexes) are large planar aromatic compounds that interact by π-π stacking with an external G-quartet of quadruplex. Porphyrins are well-known G-quadruplex ligands. We report herein a new porphyrin scaffold (meso-tetrakis(4-(N-methyl-pyridinium-2-yl)phenyl)porphyrin) able to strongly and selectively bind to G-quadruplex DNA. We show that even when this porphyrin is metallated with cobalt(III), i.e. it carries two water molecules as axial ligands on the cobalt ion, on each face of the porphyrin, the interaction occurs by a π-stacking-like mode with an external G-quartet of quadruplex DNA.

Interaction of cationic nickel and manganese porphyrins with the minor groove of DNA.

The capacity of a series of new cationic nickel and manganese metalloporphyrins to bind in the minor groove of DNA was evaluated by binding competition experiments with manganese(III)-bis-aqua-meso-tetrakis(4-N-methylpyridiniumyl)porphyrin, Mn-TMPyP, a powerful artificial nuclease when associated with KHSO(5). The four N-methylpyridiniumyl substituents on this porphyrin macrocycle are responsible for a strong binding affinity for the minor groove of AT-rich DNA. The inhibition of DNA cleavage mediated by Mn-TMPyP/KHSO(5) by the various tested porphyrins correlated with their competitive occupancy of the minor groove site of Mn-TMPyP. Introduction of long and flexible cationic substituents at the periphery of the porphyrin macrocycle precluded the interaction of the porphyrin derivative in the minor groove and resulted in low affinity for DNA. On the other hand, introduction of phenylpyridiniumyl substituents on the porphyrin macrocycle surprisingly conferred the new porphyrin derivative with a tight binding in the minor groove of a six consecutive AT base pairs sequence. These data on structural requirements for minor groove DNA binding will help the rational design of porphyrin derivatives for selective targeting of quadruplex DNA versus double-stranded DNA.

Influence of the electrochemical conversion of [(LH)Mn(II)Cl2] into [(L)Mn(III)Cl]+ on the protonic state of a phenol-containing ligand.

A bischloromanganese(II) complex [(LH)MnCl2] (1), where LH is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N'-salicylidene- ethane-1,2-diamine, has been synthesized. Elemental analysis, UV-visible, and cyclic voltammetry experiments showed that the phenol function of the ligand LH remains protonated. Exhaustive electrolysis at 1.0 V vs SCE led to the formation of the Mn(III) derivative [(L)MnCl]+ (3) with the concomitant expulsion of H+ and Cl-. The formation of the Mn(III) species was confirmed by UV-visible spectroscopy and X-ray crystallography. Complex 1 could be regenerated by the reduction of complex 3 in the presence of H+ and Cl-.

Synthesis, structure, and characterisation of a new phenolato-bridged manganese complex [Mn2(mL)2]2+: chemical and electrochemical access to a new mono-mu-oxo dimanganese core unit.

The dinuclear phenolato-bridged complex [(mL)Mn(II)Mn(II)(mL)](ClO(4))(2) (1(ClO(4))(2)) has been obtained with the new [N(4)O] pentadentate ligand mL(-) (mLH=N,N'-bis-(2-pyridylmethyl)-N-(2-hydroxybenzyl)-N'-methyl-ethane-1,2-diamine) and has been characterised by X-ray crystallography. X- and Q-band EPR spectra were recorded and their variation with temperature was examined. All spectra exhibit features extending over 0-800 mT at the X band and over 100-1450 mT at the Q band, features that are usually observed for dinuclear Mn(II) complexes. Cyclic voltammetry of 1 exhibits two irreversible oxidation waves at E(1)(p)=0.89 V and E(2)(p)=1.02 V, accompanied on the reverse scan by an ill-defined cathodic wave at E(1')(p)=0.56 V (all measured versus the saturated calomel electrode (SCE)). Upon chemical oxidation with tBuOOH (10 equiv) at 20 degrees C, 1 is transformed into the mono-mu-oxo species [(mL)Mn(III)-(mu-O)-Mn(III)(mL)](2+) (2), which eventually partially evolves into the di-mu-oxo species [(mL)Mn(III)-(mu-O)(2)-Mn(IV)(mL)](n+) (3) in which one of the aromatic rings of the ligand is decoordinated. The UV/Vis spectrum of 2 displays a large absorption band at 507 nm, which is attributed to a phenolate-->Mn(III) charge-transfer transition. The cyclovoltammogram of 2 exhibits two reversible oxidation waves, at 0.65 and 1.16 V versus the SCE, corresponding to the Mn(III)Mn(III)/Mn(III)Mn(IV) and Mn(III)Mn(IV)/Mn(IV)Mn(IV) oxidation processes, respectively. The one-electron electrochemical oxidation of 2 leads to the mono-mu-oxo mixed-valent species [(mL)Mn(III)-(mu-O)-Mn(IV)(mL)](3+) (2 ox). The UV/Vis spectrum of 2 ox exhibits one large band at 643 nm, which is attributed to the phenolate-->Mn(IV) charge-transfer transition. 2 ox can also be obtained by the direct electrochemical oxidation of 1 in the presence of an external base. The 2 ox and 3 species exhibit a 16-line EPR signal with first peak to last trough widths of 125 and 111 mT, respectively. Both spectra have been simulated by using colinear rhombic Mn-hyperfine tensors. Mechanisms for the chemical formation of 2 and the electrochemical oxidation of 1 into 2 ox are proposed.